The present invention relates to a control system for a linear synchronous motor vehicle, and more particularly to a departure control system using a simulated phase.
A known example of conventional control systems for a linear synchronous motor (hereinafter referred to as xe2x80x9cLSMxe2x80x9d) vehicle comprises, as shown in FIG. 4, a propulsion coil 61 provided along a guideway on a ground; a field coil 62a provided on a vehicle 62 so as to face the propulsion coil 61; a speed controller 63 for outputting a current command value I* computed by proportional integral operation of the deviation between a speed command value v* and the actual speed v; a converter controller 64 for performing proportional integral operation of the deviation between the current command value I* and a coil current I flowing through the propulsion coil 61 and outputting a voltage command value V* with a sine wave in synchronism with a position detecting phase xcex8p as a phase reference to indicate the position of the vehicle; a power converter 65 for outputting a three-phase output voltage V in accordance with the voltage command value V* to the propulsion coil 61 through a feeder 66; a current detector 67 for detecting the coil current I flowing through the propulsion coil 61; a cross induction line 68a arranged along the track so as to obtain information about the vehicle position; a position detector 68 for detecting a relative position of the field coil 62a to the propulsion coil 61 based on a signal generated in the cross induction line 68a and outputting the position detecting phase xcex8p; and a speed detector 69 for performing operation of an actual speed v necessary for speed control from the position detecting phase xcex8p and outputting the actual speed.
The propulsion coil 61, particularly as shown in FIG. 5A, is composed of coil sections, such as 71A1, 71B1, and 71C1 having a prescribed length and a plurality of groups of coils for propulsion therein, which are arranged on both sides of the vehicle 62 such that respective coil sections on one side are shifted by half of their length relative to respective coil sections on the other side. As shown in FIG. 5B, each coil section comprises a plurality of groups of coils for propulsion of three phases, i.e. U-phase, V-phase, and W-phase, respectively, which groups are arranged along the forward direction of the vehicle. By supplying three-phase alternating current to these groups of coils, shifting magnetic field is generated. A phase reference is predetermined by using the length of a group of coils for propulsion of 2.7 m as one cycle (360xc2x0) of an electrical angle, and information about the vehicle position is obtained by detecting the phase reference with the position detector 68.
The feeder 66 for supplying electricity, or outputting output voltage V, from the power converter 65 to each coil section consists of three feeder cables corresponding to three inverters 65A, 65B, and 65C, respectively, contained in the power converter 65. By controlling feeder section switches such as 72A1, 72B1, 72C1 . . . (omitted in FIG. 4) separately, electricity is supplied only to the three lines of coil sections in the vicinity of the running vehicle 62.
For example, when the vehicle 62 runs in the right direction as shown in FIG. 5A, three feeder section switches 72C1, 72A2, and 72B2 are closed and electricity is supplied to the coil section 71C1 through a C-line inverter 65C, to the coil section 71A2 through an A-line inverter 65A, and to the coil section 71B2 through a B-line inverter 65B, respectively. When the vehicle 62 reaches the position corresponding to the coil section 71B2, a feeder section switch 72C2 is closed while the feeder section switch 72C1 is opened, with the result that power supply is stopped for the coil section 71C1 and started for the coil section 71C2 instead.
An LSM vehicle is driven by propulsion force generated by the interaction between a magnetic field generated by the field coil 62a, which is a superconductive coil, and a magnetic field generated in the propulsion coil 61 due to the three-phase output voltage V outputted from the power converter 65. To control driving of the LSM vehicle, the position detecting phase xcex8p is inputted into the converter controller 64 as a phase reference indicating the position of the vehicle 62, and an actual speed v is computed by the speed detector 69 based on the position detecting phase xcex8p. Therefore, accurate detection of the position detecting phase xcex8p, i.e. the vehicle position, is required.
To fulfill this requirement, the cross induction line 68a is laid along the length of the track and a signal (an electric wave) is transmitted from the vehicle 62 to the cross induction line 68a. By processing a sine wave signal, which is generated in the cross induction line 68a due to the signal transmission from the vehicle 62, with the position detector 68, the position detecting phase xcex8p is obtained. Thus, substantially accurate position detection is achieved.
However, the above-described method of detecting the position of the vehicle 62 requires accurate laying of the cross induction line 68a along the length of the track and maintenance thereof as well. It leads to a large amount of labor and high cost for construction and maintenance of the vehicle position detecting system.
To solve this problem, a method of detecting the vehicle position without providing a ground installation such as the cross induction line 68a has been thought out. In this method, electromotive force induced in the propulsion coil 61 due to the running of the vehicle 62 (hereinafter referred to as xe2x80x9cspeed electromotive forcexe2x80x9d) is estimated, and a phase indicating the vehicle position (hereinafter referred to as xe2x80x9cspeed electromotive force phasexe2x80x9d) xcex8e is obtained based on the estimated value. Specifically, in the control system for an LSM vehicle shown in FIG. 4, a speed electromotive force is estimated based on the output voltage V outputted from the power converter 65, the coil current I flowing through the propulsion coil 61, and a vehicle angular speed, then a speed electromotive force phase xcex8e is computed from the estimated value of speed electromotive force.
As described above, by computing the speed electromotive force phase xcex8e and using the same as the phase reference instead of the position detecting phase xcex8p, ground installations such as the cross induction line 68a and the position detector 68 become unnecessary.
At a lower speed, however, the speed electromotive force phase xcex8e is an unstable phase because the speed electromotive force is weak. Especially, at the time of departure, the speed electromotive force phase xcex8e cannot be obtained because the speed electromotive force is not at all generated.
Then, it has been thought out that using a simulated phase as the phase reference at the time of departure when control based on the speed electromotive force phase is impossible. The simulated phase is obtained by the operation based on the current command value I* outputted from the speed controller 63. Specifically, as shown in FIG. 6, a propulsion force F is computed by an propulsion force computing unit 81 based on the current command value I*, and an acceleration a is computed by an acceleration computing unit 82 based on the propulsion force F and a running resistance D outputted from a running resistance computing unit 85. Then, a speed v is computed by a speed computing unit 83 based on the acceleration a and a simulated phase xcex8n is computed by a phase computing unit 84.
As described above, even at the time of departure when the speed electromotive force xcex8e cannot be obtained, the simulated xcex8n can be obtained by carrying out an operation based on the current command value I*. Therefore, it is possible to obtain the phase reference without ground installations such as the cross induction line 68a, by using, for example, the simulated phase xcex8n as the phase reference at the time of departure and the speed electromotive force phase xcex8e as the phase reference at a predetermined speed or higher.
However, as shown in FIG. 6, the simulated phase xcex8n is obtained merely by theoretical operation based on the current command value I* without using an actual phase reference (e.g. the position detecting phase xcex8p), the output voltage V, or the like as a feedback signal. As a result, drive control of an LSM vehicle using the simulated phase xcex8n as the phase reference, which is a so-called open loop control, is subject to disturbance and therefore prone to have unstable control characteristics.
In particular, although in computing of the propulsion force F by the propulsion force computing unit 81 and in computing of the running resistance D by the running resistance computing unit 85, various coefficients necessary for computing are determined based on the results of actual runs of a vehicle and simulations, running conditions of a vehicle actually vary each time it runs, and thus it is almost impossible to exactly match the propulsion force F and the running resistance D with the respective values at the time of actual runs, that is some errors are unavoidable. As a result, the deviation between the simulated phase xcex8n ultimately computed and the actual phase becomes substantial.
Specifically, since the simulated xcex8n different from the actual vehicle position (the actual phase) is used as the phase reference, the speed and the current command value I* suddenly change and make passengers feel uncomfortable when the phase reference is switched over from the simulated phase xcex8n to another phase (the position detecting phase xcex8p), for example, as shown in FIG. 7. Furthermore, an excessive phase deviation may cause loss of synchronism in the LSM and thereby make it impossible to control the LSM.
Wherefore, a principal object of the present invention is to provide a control system for an LSM vehicle using a simulated phase as a phase reference at the time of departure, which overcomes the above mentioned problems and realizes stable departure characteristics.
This and other objects are accomplished with a departure control system using a simulated phase in a control system for an LSM vehicle driven by propulsion force obtained by an interaction between the magnetic field produced in a propulsion coil arranged along a guideway on a ground by an output voltage outputted from power converting means and the magnetic field produced by a field coil provided on the vehicle so as to face the propulsion coil, the departure control system generating a phase reference as a vehicle position signal at the time of departure of the vehicle.
In the control system for an LSM vehicle, an output voltage is outputted to the propulsion coil by the power converting means based on the current command value I* outputted from speed control means and a phase reference in the same manner as in the above described conventional driving control system.
In this case, the phase reference as a vehicle position signal with respect to the LSM including the field coil and the propulsion coil is the relative position of the field coil to the propulsion coil indicated in the form of an electrical angle. For example, in the case of the LSM in which a movable magnetic field is produced by supplying three-phase alternating current to the propulsion coil, the distance between a U-phase coil and the field coil in the traveling direction of the vehicle is indicated in the form of an electrical angle, which is used as the phase reference.
In the departure control system according to the present invention, a simulated phase reference value is first computed by simulated phase reference value generating means by the operation based on the current command value I*. The simulated phase reference value is a theoretically computed distance (phase) the vehicle should travel when the vehicle is driven based on the current command value I* outputted from a speed controller. The simulated phase reference value is computed, for example, in the same way as in the prior art system (cf. FIG. 6). In this case, the simulated xcex8n shown in FIG. 6 corresponds to the simulated phase reference value in the present invention. This computing, however, is simply based on a predetermined theoretic computing equation without taking disturbance or the like into consideration. Accordingly, if the simulated phase reference value is used as it is, as the phase reference, problems due to the deviation between the same and the actual phase will occur as described concerning the prior art system.
Therefore, according to the present invention, the simulated phase xcex8n is computed by simulated phase generating means by adding a predetermined phase delay xcex8d to the simulated phase reference value, and the simulated phase xcex8n is outputted as the phase reference. In other words, due to addition of the predetermined phase delay xcex8d, the obtained simulated phase xcex8n is delayed from the actual phase. When control is started (that is, the vehicle is started) under this condition, the phase deviation between the simulated phase xcex8n and the actual phase becomes little due to so-called synchronizing force to make the field coil move in the synchronizing speed of the LSM. The phase delay xcex8d should be appropriately determined, for example, based on the results of actual vehicle runs and simulations so that the deviation between the simulated phase xcex8n and the actual phase is reduced due to the synchronizing force.
The above simulated phase reference value is generated by a simulated phase reference value generating means provided with a propulsion force computing unit for computing propulsion force based on the current command value I*, a running resistance computing unit for computing running resistance based on the present speed, an acceleration computing unit for computing an acceleration based on the propulsion force and the running resistance, a speed computing unit for computing a speed based on the acceleration and a phase computing unit for computing the simulated phase reference value based on the speed. The speed obtained by the speed computing unit is used as the above mentioned present speed.
According to the above described departure control system, in which the simulated phase xcex8n is computed by adding the phase delay xcex8d to the simulated phase reference value theoretically obtained by the simulated phase reference value generating means and the simulated phase xcex8n is used as the phase reference, the phase deviation between the simulated phase xcex8n and the actual phase can be substantially reduced by the operation of synchronizing force. Thus, characteristics at the time of departure such as speed characteristics and acceleration characteristics are stabilized, that is, the speed, the acceleration, the current flowing through the propulsion coil, and the like hardly change even when the phase reference is switched over from the simulated phase xcex8n to another phase, namely, the position detecting phase e p described referring to FIG. 4.
Although it is possible to reduce the phase deviation between the phase reference and the actual phase almost to zero (hereinafter referred to as xe2x80x9csynchronizexe2x80x9d) by using the simulated phase xcex8n to which the above mentioned phase delay xcex8d is added as the phase reference, the phase deviation between the simulated xcex8n and the actual phase still exists in the transition immediately after the departure, i.e. the time period until synchronization is achieved due to synchronizing force. In particular, the phase delay xcex8d is equal to the phase deviation at the time of departure when the vehicle is stopped, and the phase deviation gradually decreases after the departure by the operation of synchronizing force until synchronization is finally achieved, then the synchronous state remains thereafter.
Accordingly, in the transition immediately after the departure, the phase reference is delayed from the actual phase, which leads to the determination that the vehicle is positioned behind the actual position, with the result that a propulsion force normally necessary for the vehicle (a propulsion force in accordance with the actual phase) cannot be obtained. Propulsion force generally depends on the amount of current flowing through the propulsion coil.
To compensate for a shortage of propulsion force caused in the transition immediately after the departure, it is preferable to increase the current command value I* by a predetermined amount with current command value correcting means, output the same as a current command correction value I*c, and output an output voltage to the propulsion coil and generate the simulated phase reference value with the simulated phase reference value generating means based on the current command correction value I*c instead of the current command value I*. The predetermined amount to be increased may be appropriately selected within the range where the propulsion force in accordance with the actual phase of the vehicle can be obtained.
According to the departure control system described above, since the shortage of propulsion force caused in the transition immediately after the departure until achievement of synchronization is compensated for by increasing the current command value I* by a predetermined amount, sufficient propulsion force can be obtained immediately after the departure and thus synchronization can be achieved earlier. Once synchronization is achieved after the phase deviation gradually decreases, the current command value I* may be used as it is. It is to be noted, however, that even if the current command correction value I*c is still used after the achievement of synchronization, excessive current is not to flow through the propulsion coil because the speed controller generally compares a predetermined speed pattern corresponding to the vehicle position with the actual vehicle speed, and outputs the current command value I* based on the comparison results.
In general, when output voltage is outputted using the phase reference having a phase deviation of dxcex8 from the actual phase, the resulting propulsion force is cos dxcex8 times the propulsion force required substantially. Then, the current command correction value I*c is obtained by performing the following operation based on the current command value I* and the phase delay xcex8d with the current command value correction means.
I*c=I*/cos xcex8d
By obtaining the current command correction value I*c using the above equation, shortage of propulsion force due to the phase deviation xcex8d at the time of departure can be sufficiently compensated for and early synchronization can be achieved while keeping the speed and the acceleration stabilized.